The present invention relates to improved vertical-axis wind turbines with enhanced conversion of wind kinetic energy into mechanical energy. Vertical-axis turbines are typically of a long axis type, allowing large columns of air to be harnessed. These devices differ from horizontal-axis (propeller) type windmills which typically pivot about a vertical axis in order that they may face directly into a wind. The improvement of the invention comprises the use of lightweight materials for the construction of the components of the wind turbine. Lightweight materials such as non-metallic composite sandwich panels are preferred. The vertical-axis turbines of this invention are designed to be employed as a cost effective alternate power source in any wind condition.
Wind as a source of energy is a concept that has been promoted for some time. According to one source, there is evidence which shows that windmills were in use in Babylon and in China as early as 2000 B.C. The United States Patent and Trademark Office has granted patents on windmill devices dating back to the early to mid 1800""s. Despite the continued research and development in this age old technology, until the present invention, no windmill or wind turbine device has successfully appropriately addressed some of the most important problems which have seemingly made the harnessing of wind not economically feasible. While wind is unquestionably a large potential source of energy, estimated to be about 5 kW per acre in the United States, its variability in velocity has made it an unreliable source. Many devices such as U.S. Pat. No. 4,850,792 to Yeoman, U.S. Pat. No. 4,035,658 to Diggs and U.S. Pat. No. 2,406,268 to Terhune have relied on the ability of concentrating low to moderate winds for producing power. Others, like those shown in U.S. Pat. No. 4,834,610 to Bond and U.S. Pat. No. 4,075,500 to Oman, et al. (a horizontal-axis turbine), have accomplished the harnessing variable wind speeds by using modern variable speed governors. No device currently known to the present inventors is capable of adequately harnessing low and high-winds for power production. High winds are characterized, for purposes of discussion as currents having average velocities above 45 m.p.h., or having gusts greater than 60 m.p.h. Many devices are designed to fold and/or feather in winds reaching certain levels. Such devices are illustrated in U.S. Pat. No. 4,818.181 to Kodric, U.S. Pat. No. 4,632,637 to Traudt, and U.S. Pat. No. 3,942,909 to Yengst. These techniques, while intended to protect the structural integrity of the windmill, decrease a device""s ability to produce power. Others, such as U.S. Pat. No. 5,391,926 to Staley and Elder, attempt to harness high winds emanating from any direction for power production but low to moderate winds have been unable to produce adequate torque for continual reliable power generation. Until the present invention variable winds have been an untapped source of energy by those skilled in the relevant art.
In the past, wind driven power generators of all sorts have attempted to harness the energy present in the wind. Some have concentrated their efforts in the low to moderate wind range and suffer periodic damage from the occasional high wind while others work well in the moderate to high wind range with little or no success in harnessing low speed wind. No prior art has effectively drawn useable power from the slight breeze all the way to gale force winds. Perhaps one of the biggest reasons for the lack of all wind turbines has to do with the structural integrity of typical wind devices. By design many are lightweight, inadequately supported, and made from insufficient materials. A number of these devices are comprised of a multitude of moving parts, such as rotors, stators, vanes, shields, and the like. These parts not only compromise the integrity of the machine, but also require continuous maintenance, repair and/or replacement. For such a device, which may produce only a few kilowatts of power, the costs soon begin to outweigh the benefits. Another concept widely used is to build large multi-story wind turbines capable of producing at or near the megawatt level. Two such devices are shown in U.S. Pat. No. 3,902,072 to Quinn, and U.S. Pat. No. 3,994,621 to Bogie. It is believed that these devices would cost close to $100 million to build and several hundred thousand to maintain each year. Another example is the 1.25 MW generator installed near Rutland, Vt. This is believed to be the largest windmill ever built in the United States, having two main blades each 175 feet in diameter. This facility operated intermittently between 1941 and 1945, during the war years when most resources were being used for war efforts. In 1945 one of the blades broke due to material fatigue and was never repaired, presumably due to a lack of cost efficiency. Similar to the smaller units, these large devices become cost prohibitive on a much larger scale. The present invention solves this second problem by presenting a low cost, low maintenance, cost efficient wind turbine. While certain aspects of the design have been known, until the present invention the proper combination of elements, new and old, has not been achieved to provide a commercially viable product.
Variable wind velocity is not, of course, the only obstacle in harnessing kinetic energy from the wind. Wind direction has been another area of study and development. Wind currents are typically unpredictable, and due to topography, upper air disturbances, changing weather patterns, or seasonal variations, they rarely blow in the same direction for any substantial length of time. For this reason effective wind machines must be capable of immediately accommodating winds from a full 360 degrees. Some devices have attempted to accomplish this goal with pivoting shields, and stators or wind directing vanes. U.S. Pat. No. 4,474,529 to Kinsey, U.S. Pat. No. 537494 to Stevens et al., the Yengst patent, and many other devices illustrate such an approach. As mentioned previously, additional moving parts usually detract from a machine""s cost effectiveness. While not in the field of the present invention horizontal-axis machines typically pivot the entire rotor assembly so that it may face upwind. Still other designs leave the rotor assembly open (that is, no wind directing vanes or stators are utilized) so that winds from any horizontal direction may impart rotation upon the rotor assembly. This leaves the rotor completely open to the harshness and destructive abilities of the wind. Once again the present invention solves this problem by providing 360 degrees of wind reception, in all types of wind conditions.
One important application of a wind turbine able to respond to wind from all directions and of variable velocity is as a power generator on top of tall buildings. One reason for this is that wind velocity typically increases with altitude above the ground. For example, the wind velocity at the top of a 36 story building is on average 18 mph faster than on the ground, and is typically 45 mph faster at the top of a 70 story building. As another example, the wind velocity at the top of the Sears Tower in Chicago, Ill., averages 70 mph. This wind at the tops of tall buildings is clearly a potential power source. A wind turbine large enough to be economically useful on top of a tall building would measure about 20 feet tall by 20 feet wide. A wind turbine of this size built out of traditional materials such as xc2xd inch thick steel plates would weigh about 28,000 pounds, and additional bracing required to hold the turbine in place would weigh as much as 60,000 pounds. A problem with a turbine of this size is that it would unresponsive to light wind as it would require a wind velocity of at least 18 mph before it would begin to turn. There is also a gyroscopic effect associated with the turbine as it begins to rotate that increases with increasing rotational speed that would cause additional stress to the building in response to the torque on the turbine. In addition, traditional materials such as steel, due to its thermal conductivity, would begin to form ice on the turbine blades, which would negatively impact the smooth flow of wind through the turbine.
The present invention, in its various embodiments, recognizes and addresses these and other problems and overcomes many limitations encountered by those skilled in the art. Many devices and procedures have taught the use of folding or feathering in high wind conditions, and thus have been unable to realize the potential power of high winds. Others, such as the Staley and Elder patent have attempted to address the damaging characteristics of high winds by stressing structural integrity and durability to the point of sacrificing the ability to produce adequate torque in the low to moderate wind speed range. It is not economically feasible to build a wind turbine that can only produce mechanical power during periods of high wind. The entire range of wind conditions must be fully utilized for a wind turbine to be commercially viable. Problems such as high cost and high maintenance of most wind energy facilities exist in the field, but such problems have not been adequately addressed by those skilled in the art. While high velocity wind is a well known natural occurrence with high kinetic energy, its value in the field of vertical-axis wind turbines has not only been ignored to some extent, it has often been looked upon as a detriment. The prior art has taught away from the present invention by stressing rotor attachment and stator curvature. Rather than supplying a system which affords only an incremental increase in performance over the prior art, the present invention utilizes techniques which were not previously considered in order to achieve what may perhaps be leaps in performance compared to the prior art. Further, the present invention has achieved a more full utilization of a previously untapped precious natural resource, the wind.
The present invention discloses an improved wind turbine which provides enhanced conversion of wind kinetic energy into mechanical energy and which operates in all wind conditions, such as velocities up to 130 mph, and frequently changing wind directions. The improvement comprises the use of light weight modem building materials such as lightweight composite laminates to the reduce weight of the weight turbine and the improved thermal properties of such materials decrease the tendency of turbine blades to form ice. Non-metallic materials such as fiberglass or carbon fiber composite materials are as strong as steel but with only a fraction of the weight. The preferred materials are honeycomb sandwich panels that typically feature a honeycomb core manufactured from an aramid fiber with various non-metallic face layers, such as epoxy, fiberglass, phenols, and kevlar. Alternatively, lightweight metals such as aluminum can be used in the construction of the honeycomb core. The face layers can be laminated.
The wind turbine also provides a reliable and effective means for directing air currents into and out of the rotor cage assembly. Rather than supplying a system which affords only an incremental increase in performance and design over the prior art, the present invention utilizes combinations and techniques which were not previously considered to achieve an increase in performance unparalleled by the prior art. This invention serves to operate with a minimum number of movable parts and systems, to optimize potential power production by allowing energy from high winds to be harnessed as well as low and moderate winds, and to optimize air current intake and exhaust by providing immediate accommodations to winds from any given direction.
In general terms, the invention involves various embodiments of a vertical-axis wind turbine. Many of the elements of this device achieve several different objectives which, when combined, act to achieve the mentioned increases in performance. In the preferred embodiment, the invention discloses stationary stators for more effectively directing currents into the rotor cage assembly to impart a higher rotational velocity and greater torque upon the turbine shaft through some torque generating elements such as the rotor blades. In addition, the stationary stators provide a structural integrity necessary for operation during high wind conditions. This aspect also prevents the disruption of rotation by shielding the rotors from winds counter-directional to their rotation which may occur as the wind shifts. The present wind turbines comprise stator blades which are straight and wherein the stator blades are offset b optimal offset angle so that there is a minimal effect on the loss of wind kinetic energy.
Importantly, the invention breaks from several time honored traditions in harnessing wind. By recognizing and utilizing the potential energy of all winds, and by designing an apparatus with resistance to the destructiveness of these winds during standard operation the present invention achieves its goals.
Accordingly, the present invention provides an omni-wind, vertical-axis turbine which can be employed in many different environments including on the tops of tall buildings. The stated invention acts to convert wind currents into mechanical energy which energy may then be transferred from a turbine or the like to be used to directly act upon a water pump, or to drive an electrical generator (or more generically an energy-utilizing device) for use as an alternate power source. The turbine may be equipped with any number of rotors and stators which interact with the variable wind currents during operation. In addition, a minimum number of moving parts is used to increase reliability, to decrease maintenance, and to decrease production costs.
It is an object of the present invention to provide a wind turbine design and construction which is capable of operation with enhanced efficiency in a variety of wind conditions. Such conditions include, but are not limited to, winds from any direction which possess a horizontal component, even where such wind direction is capable of frequent changes, winds reaching velocities of 130 m.p.h. or more, and winds with continuously changing velocities. It is an object that the present invention be capable of standard operation during these conditions without any need for employing folding and feathering techniques, or a speed control or braking system.
It is another object of the present invention to provide an improved design which is capable of immediately accommodating winds from any direction having a horizontal component, as stated earlier. It is an object that this immediate readiness of the present invention be achievable with no moving parts.
It is, therefore, an object of the present invention to provide a design which utilizes a minimum of moving parts for improved reliability. It is an object that necessary maintenance and replacement of any parts should be minimized, and the durability of the entire apparatus be vastly improved. Furthermore, an object of this invention is to provide an improved wind turbine which can be used in various environments including tall buildings and which the turbine elements which resist icings.
Naturally, further objects of the invention are disclosed throughout other areas of the specification and claims.